137Cs and 239,240Pu activity concentrations distribution in waterlogged and non-boggy soils of Lithuania

Vertical distributions of 239,240Pu and 137Cs activity concentrations in the waterlogged and non-boggy soil cores sampled in the vicinity of Vilnius City and in the Varėna District were analyzed. The radionuclides appeared in the soils mainly as a result of the fallout after the nuclear weapon testing in atmosphere in 1960s and due to the Chernobyl NPP accident in 1986. The deposited radionuclides on the surface of waterlogged soils on the shores of lakes experienced processes of translocation and accumulation, therefore their total activity in the column differs from the activity in non-boggy soils. The mobility of plutonium is the highest in waterlogged organic-rich soils. Clay in the waterlogged soil significantly limits the migration of radiocesium and does not affect noticeably the mobility of plutonium. Compared with radiocesium, the mobility of plutonium in non-boggy soils is somewhat limited. So, in waterlogged and non-boggy soils, the radionuclide mobilizing factors act in the opposite directions for radiocesium and plutonium. A clear correlation between the radionuclide activity and soil organic matter content was not observed. The investigation showed that radionuclide mobility can be determined by studying radionuclide physicochemical forms in the soil, vertical profiles of radiocesium to plutonium ratios, soil composition as well as its oxidation regime.